Thermionic voltmeter



' R. A. HEISING. THERMIONIC VOLTMETER. APPLICATION FILED JULY 30. {519KReissued Oct. 17, 1922; r 1 5 ,469.

hue/avianfig/mand A f/e/is/h M A/Vj/ Reissuea Oct. 17, 1922.

UNITED STATES-PATENT OFFICE.

RAYMOND A. EEISING, OF EAST ORANGE, NEW JERSEY, ASSIGNOR, BY MESNEASSIGN- MEN'IS, 'IO WESTERN ELECTRIC COMPANY, INCORPORATED, ACORPORATION OF NEW YORK.

.THERMIONIC VOLTMETER.

Original 110. 1,282,919, dated July 10, 1917, Serial No. 49,253, filedSeptember 7, 1915. Applieatiortor reissue filed July 30, 1919. SerialNo. 314,384.

To all whom. it may concern:

Be it. known that I, RAYMOND A. HEISING, a citizen of the United States,residing at East Orange, in the county of Essex and State of New Jersey,have invented certain new and useful Improvements in ThermionicVoltmeters, of which the followin is a full, clear, concise, and exactdescription.

This invention relates to apparatus for the measurement of voltage.

Its object is to measure. the voltage between two points of anelectrical network without taking power from that network and withoutintroducing frequency errors. A further object is to measure a direct oralternating voltage without the necessity for previous calibration ofthe instrument, which calibration in the case of high frequencymeasurements is often unsatisfactory and diflicult.

These objects are accomplished by con necting the input circuit of athermionic rectifier between the net work terminals across which thevoltage is to be measured, and allowing the resulting rectified currentin the output circuit to actuate an indicating instrument. a

The nature of thisinvention and its method of use will be more fullyexplained in connection with the drawing, which represents the circuitarrangement of the invention.

In the drawing, 1 represents a source of voltage to be measured and 2 isa thermionic rectifier of the audion type upon which is impressed thevoltage which it is desired to measure. This rectifier consists of aheated v electron-emitting cathode 3, a cool anode 5 and auxiliaryelectrode 4 usually located between the cathode and the anode. Theseelements are sealed in a vessel which is 'exhausted as thoroughly aspossible so as to remove practically all the gas. The hot cathode givesofi electrons, which, due to the electric field set up between anode andcathode by means of battery 7, are driven across the evacuated space andstrike the anode. A current of electrons therefore flows between thesetwo elements and its circuit is completed externally through the batteryand the current indicating instrument 6. This circuit is called theoutput circuit of the rectifier, and since electrons can pass only fromcathode 3 to anode 5 and not in the reverse direction, the current .tochange the number of the electrons passing to anode 5, and, therefore,the intensity of the current in the output circuit; further, if the gridis maintained at a lower potential than the cathode, no electrons canflow to the grid and consequently no current can flow in the inputcircuit which comprises the electrical path 1, 13

(lower), .10, 3, 4, 13 (upper), 1. Under these conditions the inputcircuit requires practically no power to produce changes in the outputcurrent. To maintain the grid at a potential lower than that of thecahode is one function of the battery 8, which in combination with theresistance 9 and contact maker, 10 supplies an adjustable voltage acrossthe input terminals of the rectifier. The intensity of current in theoutput circuit is determined completely by the voltage impressed uponits input terminals so long as the grid potentialis maintained negative;in particular, if the voltage across the input circuit is madesufficiently large, so as to force a sufliciently large negative chargeupon the grid 4, the current in the output circuit may be reduced tozero and thus no indication will appear upon the instrument 6.

These facts furnish the basis of a method for measuring an unknownvoltage, either alternatin or direct, without previous calibration o theinstrument in terms of a known voltage of the same type. The method ofuse for this purpose is as follows: The switch 11 is thrown to the.position 12, 12, in which position the input circuit is closed throughthe conductor 14. The contact 10 is now adjusted until the voltage overthe input circuit is just suflicient to reduce the current in the outputcircuit to zero as indicated by the instrument 6. The switch 11 is nextthrown to the position 13, 13, in which position a source 1 of voltageto be measured is connected into the input will, therefore, cause aunidrectionalcurrent to flow in the output circuit once'every cycle andthe average value of this current will be indicated by 6. The contact 10is now moved to some other position 10'. in which 'the outv ut currentagain falls to zero be'- lcauseo the increase in negative voltagempresed from battery 8 in the new position of I contact 10. In otherwords, the increase in I it voltage impressed from battery 8 is justsufli-.

' cient to make. the resultant maximum negaof potential over t tiveinput voltage the same as inthe case when t the maximum value of thealternating volt.-

' age to be measured. In the practical-use of the device, the resistance9 should .be marked .ofi in terms of the fall of potential alon itslength as in any potentiometer system 0 measurement. 'If a directvoltage is to be measured instead of an alternating one, the

only precaution to be observed is that they are that measurements, 0alternating volt- ..ages maybemade by a direct current poten- "tiometer'method, which is of-considerable value in measurements of alternatingvoltages of high frequency, that the device takes practically no powerfor its operation, and also that voltages of widely difi'erentfrequencies may be measured with the same accuracy. ThlS last statementis sup orted by v the fact that thermionic amplifiers ave been found toive no noticeable distortion when used in te ephonyor, in radiooperation.

-the output circuit of said rectifier, an adjustable source ofelectromotive force in the input circuit of said rectifier, andterminals for impressing upon said linput circuit a volta e-to bemeasured.

I 2. n combination, a thermionic rectifier comprising a hot cathode, acool anode and an auxiliary electrodein an evacuated vessel, a currentindicating instrument and a battery connected in series between saidanode and said cathode, terminals in the input circuit of said rectifierto which terminals may be a plied a voltage to be measured, and an' ajustable source of electromotive force connected, in series with saidterminals, between said cathode and said auxiliary electrode.

3. A voltmeter comprising a vacuum tube having input and outputcircuits, a current indicating instrument in the output circuit of-saidvacuum tube, an adjustable source of electromotive force in the inputcircuit e 'source 1 was not in circuit. Thisincrease in voltage'measured by the fall.

he resistance 9 between thepoints 10 and 10', is thereforeequal to ofsaid vacuum tube and for'im- I I 4. An" electrical measuring instrumentcomprising a vacuum tube device havin .a cathode, an anode, a controlelectrode an a source of space current, means for connecting anelectrical source of unknown value to certain of said electrodes, ameasuri instrument connected to said device,-aiid means formaking thepotential of-said control' electrode suchas to reduce the space currentbetween anode and cathode subpon said input circuit a voltage tobemeasured.

stantially to zero while measurements are I beingkmade wherebysubstantially no power is ta enf from the unknown source at that time]5. A voltmeter comprising an electron v discharge device having inputand, output circuits, a current indicating instrument in said outputcircuit, an adjustable source of electromotive force in said inputcircuit, and

terminals for timpressin on one of said circuits an alternating 'vo tagethe peakvalue of which is to be measured."

6 The method of measurin voltage which comgeises applying said votage'to a vacuum tu device having a control electrode and an outputcircuit, applying a known voltage to the control electrode of saiddevice, measuring the combined effect of said voltages in the outputcircuit of said device, and comparin known voltage and'said efl'ect.witlia previously determined characteristic of said 100 devic 7. Themethod of measurin voltage the values of said 1 vacuum tube having anoutput circuit, an

input circuit and aplurality of sources of same efi'ect in said outputcircuit both when the operation of the tube is influenced and when notinfluenced by the voltage to. be measured.

8. The method of measuring volta ewhich comprises comparin the grid votages necessary to produce t e same effect in the output circuit of avacuum tube both when the operation of the tube is influenced and whennot influenced bythe electrical voltage to be measured;

9. he method of measuring voltage which comprises applying said voltageto a vacuum tube device avlng a cathode, an anode, a control electrode,and a source of space current, and making the potential of said controlelectrode such as to reduce the.

potential, and comparing the volta es nec- -essary in said input circuitto pro uce the tentials to the input and output circuits of a vacuumtube, noting an electrical efl'ect in said output circuit, applyingsaidalternating current voltage to one of said circuits and comparing aneffect produced thereby in said output circuit with said firstmentionedeffect. n

11. The method of determining the magnitude of a voltage of analternating current, which comprises applying steady po- 10 tentials tothe input'and output circuits of a vacuum tube, noting an electricaleffect in said output circuit, applying said alternating current voltageto said input circuit and comparing an effect produced thereby in 15said output circuit with said first mentioned efi'ect.

RAYMOND A. HEISING.

